For subsea intervention operations, access to the well is gained by way of a production tube that is connected to a wellhead/christmas tree. Often, a riser is extended horn a wellhead to the ocean surface and the production tube is extended there through to the wellhead/christmas tree. An annulus is between the outside of the production tube and the inside of the riser. During intervention, flowback of well fluids can take place in the production tube. The well fluids are often hot and can be up to at least approximately 450° F.
For intervention a subsea test tree in connection with a subsea control module is integrated with the production tube and is used to control flow by way of various flapper and ball valves in the subsea test tree. The subsea control module can include accumulators. The accumulators can be pressure balanced accumulators. An accumulator is a device that stores potential energy. Often the potential energy is stored by way of compressed fluid, e.g., gas such as nitrogen or helium that transfers energy to a non-compressible fluid by way of a piston. The non-compressible fluid can be used to actuate tools by way of hydraulic, pressure. Valves (such as solenoid valves) can be used to control the output of the hydraulic fluid from the accumulator. Such solenoid valves can be controlled by a subsea electronics module. The subsea electronics module can be located proximate the subsea control module and integrated therewith. The subsea electronics module can also be located at surface and connect to the solenoid valves remotely. The subsea electronics module can receive signals electrically by wire, by acoustic transmission, by optical signals, or by pressure pulses.
Issues can arise with respect to deep water operations where ambient pressure is very high. In those cases the potential energy stored in the gas is less able to overcome the ambient pressure to perform the desired work. In those cases, pressure balanced accumulators can be used. Pressure balanced accumulators connect with the ambient pressure to exert pressure on the gas to compensate for the depth and ambient pressure.